Drill pipe

ABSTRACT

A drill pipe having a length of conduit having a first diameter, a first and a second end portion, where each end portion has a second diameter greater than the first diameter. An enlarged portion is located between and spaced from the first and second end portions, where the enlarged portion comprises a central section which has a third diameter greater than the first diameter. The central section has a substantially smooth external surface, and two end sections, one end section at either end of the central section, which vary in diameter between the first and the third diameter. One of the end sections has a spiral formation thereon.

The invention relates to drill pipe and, in particular, drill pipe foruse in drilling boreholes, such as oil and/or gas wells.

Modern drilling techniques in the exploration of oil and gas permit thedrilling of boreholes which have a large angle of deviation from thevertical, and in some cases boreholes may be horizontal or close to thehorizontal. Such boreholes are known as lateral wells. However, duringdrilling of a lateral well, the drill cuttings tend to accumulate on thelower side of the hole and it is difficult to flush the drill cuttingsout of a lateral well with the normal drilling fluid flow between thedrill string and the inside surface of the borehole.

Accordingly, in recent years proposals have been made for enhancing theagitation of the drill cuttings within lateral wells to help preventaccumulation of the drill cuttings on the lower side of the borehole.

Some of these proposals include forming upsets on the drill pipe andputting spiral formations on the surface of the upsets to agitate thedrill cuttings in the lower section of the well as the drill pipe isrotated. However, this type of drill pipe has the disadvantage that itcan tend to cut into the side wall of the bore hole as it rotates.

In accordance with present invention, a drill pipe comprises a length ofconduit having a first diameter, a first and a second end portion, eachend portion having a second diameter greater than the first diameter,and an enlarged portion located between and spaced from the first andsecond end portions, the enlarged portion comprising a central sectionhaving a third diameter greater than the first diameter and the centralsection having a substantially smooth external surface, and two endsections, one end section at either end of the central section, whichvary in diameter between the first and the third diameter, and one ofthe end sections having a spiral formation thereon.

Preferably, the spiral formation is located between the central sectionand the upper end of the drill pipe.

Preferably, the external surface of the central section is asubstantially cylindrical surface.

Typically, three of said enlarged portions may be provided on the drillpipe.

Preferably, the other end section may comprise a curved surface whichmay be convex and is typically radiused.

Alternatively, the other end section may typically comprise a linearlysloping surface.

Preferably, the spiral formations are deeper and/or wider adjacent thecentral section.

Preferably, the end section in which the spiral formations are formedhas a concave shape.

Alternatively, the end section in which the spiral formations are formedmay comprise a curved surface which may be convex and is typicallyradiused.

Examples of a drill pipe in accordance with the invention will now bedescribed with reference to the accompanying drawings, in which:

FIG. 1 is a side view of a length of drill pipe; and

FIG. 2 is a side view of a section of a length of drill pipe.

FIG. 1 shows a side view of a length of a drill pipe 1 which comprises atube section 2 which has a first diameter and a first enlarged endportion 3 having a second diameter at the upper end which includes athreaded box connection 4, and a second enlarged end portion 5 which isthe same diameter as the portion 3 at the lower end which has a threadedpin connection 6. The threaded box connection 4 and threaded pinconnection 6 permit the drill pipe 1 to be connected to other lengths ofdrill pipe (not shown) to form a drill string for drilling a borehole,such as an oil/or gas well.

The tube 2 also has an enlarged central portion 7 with a centralcylindrical surface 8 which is parallel to the exterior walls of thetube 2 and the longitudinal axis of the drill pipe 1. The cylindricalsurface 8 is smooth and is connected to the tube 2 at its upper end by aconcave surface 9 and to the lower portion of tube 2 by a convex surface10. Located in the concave surface 9 are a number of spiral formations11 which are cut out of the concave surface 9.

The drill pipe 1 shown in FIG. 1 is truncated and the full length ofdrill pipe 1 would typically have three enlarged central portions 7spaced along its length between the enlarged end portions 3, 5.Preferably, two of the enlarged central portions 7 have a spiralformation 11 formed in one direction around the circumference of theconcave surface 9, and the third enlarged central portion 7 having aspiral formation 11 formed in the other direction.

In addition, hard banding may be applied to the enlarged portion 7, ifdesired.

An advantage of the drill pipe 1 is that the cylindrical surface 8 issmooth which helps prevent the enlarged section biting into the sidewalls of the bore hole during drilling. However, the spiral formations11 help to promote agitation of drill cuttings within the well tomitigate the problems of drill cuttings collecting on the lower side ofthe well. Typically, the spiral formations 11 would be deeper and wideradjacent the cylindrical surface 8 than adjacent the tube 2.

In addition, the maximum diameter of the enlarged portion 7 is typicallyless than or equal to the diameter of the enlarged end portions 3, 5.

FIG. 2 shows a second example of an enlarged central portion 15 whichcan be incorporated into a length of the drill pipe 1 shown in FIG. 1 inaddition to, or instead of the enlarged central portion 7 of FIG. 1.

The enlarged central portion 15 of FIG. 2 has a similar centralcylindrical surface 8 to that of FIG. 1. However, the centralcylindrical surface 8 of FIG. 2 is connected to the tube section 2 atits upper end by a convex and radiussed surface 17, into which are cutsix spiral formations 19. The central cylindrical surface 8 is connectedat its lower end to the tube 2 by a linearly sloping section 21.

As the upper end has a convex and radiused surface 17, the invention hasthe advantage that a greater surface area of metal may be scooped awayto form the spiral formations 19, which increases the efficiency of theinvention by causing greater turbulence, in use.

The longitudinal length of each of the linearly sloping section 21,cylindrical surface 8 and the convex and radiussed section 17 is 9″. Fora tube whose diameter at section B is 5″, the diameter of thecylindrical surface 8 is 6¾″, and for a tube whose diameter at section Bis 6⅝″, the diameter of the cylindrical surface 8 is 8¼″.

Modifications and improvements may be incorporated without departingfrom the scope of the invention.

What is claimed is:
 1. A drill pipe comprising a length of conduithaving a first diameter, a first and a second end portion, each endportion having a second diameter greater than the first diameter, and anenlarged portion located between and spaced from the first and secondend portions, the enlarged portion comprising a central section having athird diameter greater than the first diameter and the central sectionhaving a substantially smooth external surface, and two end sections,one end section at either end of the central section, which vary indiameter between the first and the third diameter, and one of the endsections having a spiral formation thereon.
 2. A drill pipe according toclaim 1, wherein the spiral formation is located between the centralsection and the first end portion of the drill pipe, where the first endportion is an upper end of the drill pipe, in use.
 3. A drill pipeaccording to either of claims 1 or 2, wherein the external surface ofthe central section is a substantially cylindrical surface.
 4. A drillpipe according to claim 1 wherein three enlarged portions are providedon the drill pipe.
 5. A drill pipe according to any of claims 1, 2 or 4,wherein the other end section comprises a linearly sloping surface.
 6. Adrill pipe according to claim 1 wherein the other end section comprisesa curved surface which is convex.
 7. A drill pipe according to claim 1,wherein the other end section comprises a curved surface which isradiused.
 8. A drill pipe according to claim 1, wherein the spiralformation is deeper and/or wider adjacent the central section.
 9. Adrill pipe according to claim 1, wherein the end section in which thespiral formation is formed has a concave shape.
 10. A drill pipeaccording to claim 1, wherein the end section in which the spiralformation is formed comprises a curved surface which is convex.
 11. Adrill pipe according to claim 1, wherein the end section in which thespiral formation is formed comprises a curved surface which is radiused.12. A drill pipe according to claim 1, wherein the third diameter of theenlarged portion is less than or equal to the second diameter of the endportions.
 13. A drill pipe according to claim 1, wherein the drill pipecomprises a plurality of enlarged portions spaced along its length. 14.A drill pipe according to claim 13, wherein one or more of the enlargedportions have a spiral formation formed in one direction around thecircumference of the one end section, and one or more of the enlargedportions have a spiral formation formed in the other direction.